This invention relates generally to a device for holding a portion of a saw chain during sharpening of the chain cutters. The device is intended to rest in a vise having opposed movable jaws so that tightening of the vise will cause the holding device to firmly grip the saw chain while permitting access to the chain cutters for sharpening.
In order to properly sharpen the cutters of a saw chain it is necessary to hold the cutters firmly in place while drawing a file across the cutters at the appropriate angle. Since the shape of the chain is irregular, it is difficult to grip the chain in a manner firm enough to prevent wobble in the cutters as the file is moved back and forth.
One approach taken in the prior art has been to leave the chain mounted on the saw and clamp the saw plate in place while filing the chain cutters. This approach is described in U.S. Pat. No. 3,029,663. While the '663 approach may eliminate all movement in the saw plate itself during sharpening of the cutters, the cutters will nevertheless be subject to excess wobble within the track of the plate.
Another, somewhat more promising approach, has been to clamp the flat drive chain cogs which protrude below the cutter train of the saw chain during sharpening of the cutters. A number of variations on this approach are represented in the following U.S. Pat. Nos.: 2,413,919; 2,627,191; 2,798,385; 3,013,448; 3,083,591; and 3,114,275. Although this approach certainly minimizes cutter wobble during sharpening, it fails to reduce this problem to a level which will insure maximum cutter sharpness and accuracy.
The failure of the latter prior art clamping arrangement to eliminate objectionable wobble during sharpening is believed to arise from the relatively small cog area available for clamping the saw chain. It probably also results from the spacing between the cutter edge being filed and the clamped cog which produces a torque arm at the point of retention. Whatever the source of this problem, the fact remains that notwithstanding its wide availability in the patent art, this prior approach has not received wide acceptance in the marketplace.
In yet another alternative approach, the irregular outside faces of the saw chain are clamped in lieu of either the drive cogs or the saw plate. This approach, which is illustrated in U.S. Pat. No. 2,824,469, is highly undesirable because the irregular outside faces of the chain cannot be firmly clamped by the flat clamp plates utilized in the '469 device. Thus, again the chain cutters will wobble during sharpening, impairing cutter sharpness and accuracy and precluding commercial acceptance of this approach.